Method for the production of a multi-part piston for an internal combustion engine

ABSTRACT

A multi-part piston for an internal combustion engine has an upper piston part having a piston crown, and a lower piston part. The lower piston part has pin boss supports and pin bosses connected with them and the upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses. The cavity has a separate cooling oil collector that has at least one cooling oil opening. The piston is produced by manufacturing the upper piston part and lower piston part, inserting the cooling oil collector into the upper piston part or lower piston part, and joining the upper and lower piston parts together by friction welding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 12/587,960 filed Oct. 15, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 12/381,842 filed on Mar. 17, 2009, which claims priority from DE 10 2008 055 910.5 filed on Nov. 5, 2008. Applicants also claim priority under 35 U.S.C. 119 of German Application No. 10 2009 032 865.3 filed on Jul. 14, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multi-part piston for an internal combustion engine, having an upper piston part that has a piston crown, and a lower piston part. The lower piston part has pin boss supports and pin bosses connected with them, and the upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The present invention furthermore relates to a method for the production of such a piston.

2. The Prior Art

A multi-part piston is disclosed, for example, in EP 1 222 364 B1. This piston has an outer circumferential cooling channel and an inner cooling chamber whose cooling chamber bottom is provided with an opening. This opening allows cooling oil to flow away out of the inner cooling chamber in the direction of the piston pin, in order to lubricate the piston pin and to intensify the cooling effect by means of effective cooling oil circulation. In order to achieve this goal, the opening in the cooling chamber bottom cannot be too large, because then, the cooling oil would no longer flow away in a metered manner, and effective cooling oil circulation would thereby be impaired. This means that the cooling chamber bottom is configured essentially as a relatively wide and thin circumferential ring land that extends approximately in the radial direction, in the upper region of the lower piston part. However, such a structure is difficult to produce. In the case of a forged lower piston part, in particular, there is the additional problem that when using a forging method, only a very thick and heavy cooling chamber bottom can be produced, due to forging tolerances and production restrictions.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a multi-part piston as well as a method for its production, which guarantees a good cooling effect of the cooling oil as well as effective lubrication of the piston pin, and, at the same time, is as simple as possible to produce as a light piston, also in the form of a forged piston.

This object is accomplished by a piston having a piston crown, and a lower piston part with pin boss supports and pin bosses connected with them. The upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses. The cavity is provided with a separate cooling oil collector that has at least one cooling oil opening. The method according to the invention is characterized by the following method steps: producing an upper piston part having a piston crown as well as an inner and an outer support element, producing a lower piston part having pin boss supports and pin bosses connected with them, as well as having an inner and an outer support element; inserting a separate cooling oil collector, having at least one cooling oil opening, into the upper piston part or the lower piston part, in the region of each of their inner support elements; connecting the upper piston part and the lower piston part in such a manner that each of the inner and outer support elements delimit an outer circumferential cooling channel and a cavity that is open toward the pin bosses and provided with the cooling oil collector.

According to the invention, an inner cooling chamber and thus a cooling chamber bottom in the piston are therefore eliminated. The problem of producing a circumferential ring land that extends approximately in the radial direction, as a relatively wide and thin region, is therefore completely eliminated. The upper piston part and the lower piston part of the piston according to the invention can therefore also be produced as forged parts, in a relatively simple manner, and as comparatively light components. The piston according to the invention and the production method according to the invention are thus also characterized by clearly improved economic efficiency. In this connection, the cooling oil collector serves to optimize the cooling effect of the cooling oil, particularly below the piston crown. The at least one cooling oil opening in the cooling oil collector provided according to the invention also allows significantly better and more precise metering of the cooling oil that flows away in the direction of the piston pin, so that the lubrication of the piston pin is also improved, as compared with the pistons known in the state of the art. Since the cooling oil collector can be produced and installed as a very simply structured and light component, the economic efficiency of the piston according to the invention, and of the production method according to the invention, remains unimpaired.

In a preferred embodiment of the piston according to the invention, the upper piston part and the lower piston part are connected with one another by a friction welding method that produces a friction weld bead, at least by way of their inner support elements, and the cooling oil collector is held between the friction weld beads and pin boss supports. As an alternative, the cooling oil collector can also be held between the friction weld beads and the underside of the piston crown. Positioning of the cooling oil collector in the cavity can thus be selected as desired, and can take place both above and below the friction weld beads, depending on the requirements of an individual case. The friction weld beads furthermore ensure particularly secure axial support of the cooling oil collector.

A possible embodiment of such a cooling oil collector consists in that the cooling oil collector has a flange, or edge with at least two elastic spring tongues disposed on the outer edge. In the latter case, the slits that delimit the spring tongues can serve as cooling oil openings, at the same time.

If the cooling oil collector is held between the friction weld beads and the pin boss supports, the edge or the tongues are preferably bent axially upward, and either touch the friction weld bead or rest against it or engage behind it. In the case that the cooling oil collector is held between the friction weld beads and the underside of the piston crown, the edge or the tongues are bent axially downward, and touch the friction weld bead or rest against it or engage behind it. In this manner, particularly reliable securing of the position of the cooling oil collector in the cavity, able to withstand stress, is achieved.

Additional securing of the position of the cooling oil collector can be achieved by a resilient support element on the side of the cooling oil collector facing the piston crown, which element supports itself on the underside of the piston crown.

In a preferred embodiment, the support element can have at least two, preferably three, but also more than three spring arms that support themselves on the underside of the piston crown. The cooling oil collector and the support element can be configured in one piece or in multiple pieces. In the latter case, the support element can be attached to the cooling oil collector in any desired manner, for example by means of screwing, riveting, pressing, welding, soldering and the like.

The cooling oil collector can be made from any desired material, but it is practical if the collector is configured as an at least partially spring-elastic component. In this case, it can be held in one of the two components before the upper piston part and the lower piston part are connected, under spring bias. A suitable material is, for example, a spring steel sheet. In the simplest case, the cooling oil collector has an essentially round shape and can be provided with a slight curvature.

The cooling oil collector preferably has two or more cooling oil openings, so that a very precisely metered amount of cooling oil can flow away out of the cavity, in the direction of the piston pin.

The at least one cooling oil opening in the cooling oil collector can be configured as a usual, round opening, or, for example, also as a slit that is disposed at the edge of the cooling oil collector or extends inward from the edge of the cooling oil collector.

The upper piston part and/or the lower piston part can be cast parts or forged parts, and can be produced, for example, from a steel material, particularly a forged steel.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings, wherein similar reference characters denote similar elements throughout the several views:

FIG. 1 shows a section through a first embodiment of a piston according to the invention;

FIG. 2 shows the piston according to FIG. 1 in section, rotated 90° as compared with FIG. 1;

FIG. 3 shows a section through a second embodiment of a piston according to the invention;

FIG. 4 shows the piston according to FIG. 3 in section, rotated 90° as compared with FIG. 3;

FIG. 5 shows a perspective representation of the cooling oil collector according to FIGS. 3 and 4; and

FIG. 6 shows an enlarged representation of a detail from FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in detail to the drawings, FIGS. 1 and 2 show a first exemplary embodiment of a piston 10 according to the invention. Piston 10 is composed of an upper piston part 11 and a lower piston part 12, which, in the exemplary embodiment, are forged from a steel material. Upper piston part 11 has a piston crown 13 having a combustion bowl 14, as well as a circumferential top land 15 and a circumferential ring belt 16. Lower piston part 12 has a piston skirt 17 and pin bosses 18 having pin bores 19, for accommodating a piston pin (not shown).

Upper piston part 11 has an inner support element 21 and an outer support element 22. Inner support element 21 is disposed on the underside of piston crown 13, circumferentially, in ring shape, and has a joining surface 23. Outer support element 22 of upper piston part 11 is formed below ring belt 16, and has a joining surface 24.

Lower piston part 12 also has an inner support element 25 and an outer support element 26. Inner support element 25 is disposed on the top of lower piston part 12, circumferentially, and has a joining surface 27. Outer support element 26 is formed as an extension of piston skirt 17 in the embodiment shown, and has a joining surface 28. Pin boss supports 32 for connecting the pin bosses 18 are provided below inner support element 25 of lower piston part 12.

Upper piston part 11 and lower piston part 12 are joined in known manner, by means of a friction welding method, whereby joining surfaces 23 and 27, and 24 and 28, respectively, are connected with one another.

Upper piston part 11 and lower piston part 12 form an outer circumferential cooling oil channel 29. In this connection, ring belt 16 and outer support element 22 of the upper piston part 11 as well as outer support element 26 of lower piston part 12 delimit outer cooling channel 29 toward the outside. Inner support element 21 of the upper piston part and the inner support element 25 of the lower piston part delimit the outer cooling channel 29 toward the piston interior. Inner support element 21 of upper piston part 11 and inner support element 25 of lower piston part 12 delimit a cavity 31 that is open toward pin bosses 18, which cavity is disposed essentially below piston crown 13.

In the embodiment shown, cooling oil channels 33 are provided in inner support element 21 of upper piston part 11, which connect outer cooling channel 29 with cavity 31. Cooling oil channels 33 run at an angle downward, in the direction of cavity 31, proceeding from outer cooling channel 29. Of course, cooling oil channels 33 can also be disposed in the inner support element 25 of lower piston part 12, and/or can run at an angle upward, in the direction of cavity 31, proceeding from outer cooling channel 29.

As a result of the friction welding process for connecting upper piston part 11 and lower piston part 12, friction weld beads 34 project both into cavity 31 and into outer cooling channel 29.

Cavity 31 is provided with a cooling oil collector 35. Cooling oil collector 35 is produced from a spring steel sheet, has an essentially round shape, is provided with a slight curvature, approximately in the shape of a flattened dome, and has a thickness of approximately 0.8 mm. It has a circumferential spring-elastic flange 36 and cooling oil openings 37. Flange 36 is provided with slits 38, which both increase the elasticity of flange 36 in the radial direction and serve as additional cooling oil openings. Cooling oil collector 35 is held between pin boss supports 32 and friction weld bead 34, in the region of lower piston part 12, and supports itself on pin boss supports 32 in the direction of pin bosses 18, and on friction weld beads 34 in the direction of upper piston part 11. Cooling oil collector 35 is disposed in such a manner that its curvature is directed toward upper piston part 11. Depending on the placement of the cooling oil collector 35 in cavity 31, the curvature can also be directed toward pin bosses 18.

Of course, cooling oil collector 35 can also be disposed in the region of upper piston part 11, so that it supports itself both on friction weld beads 34 and in the region of the underside of the piston crown 13. In this case, it is practical to dispose cooling oil channels 33 in the inner support element 25 of lower piston part 12.

Cooling oil collector 35 serves to collect cooling oil that passes through cooling oil channels 33, out of outer cooling channel 29, into cavity 31, and to guide it in the direction of the underside of the piston crown 13, particularly by means of the shaker effect that occurs during operation, in order to increase the cooling effect in this region. Cooling oil openings 33 make it possible to guide a defined amount of cooling oil in the direction of the piston pin (not shown) accommodated in pin bores 19, in order to improve its lubrication.

For assembly of piston 10 according to the invention, first upper piston part 11, lower piston part 12, and cooling oil collector 35 are produced as separate components. In the exemplary embodiment, cooling oil collector 35 is inserted into lower piston part 12, in the region of the inner circumferential support element 25, and held there under spring bias, with force fit. Subsequently, upper piston part 11 and lower piston part 12 are connected with one another, by a friction welding method, by way of joining surfaces 23, 27 and 24, 28, respectively, in such a manner that cooling oil collector 35 supports itself and is held both on friction weld bead 34 that has formed and on pin boss supports 32.

The inner cooling chamber having a cooling chamber bottom in the form of a wide, radially circumferential ring land, which is required in the state of the art, has therefore been eliminated.

FIGS. 3 and 4 show another exemplary embodiment of a piston 110 according to the invention. Piston 110 essentially corresponds to piston 10 according to FIGS. 1 and 2, so that structural elements that agree with one another are provided with the same reference numbers.

The significant difference consists in cooling oil collector 135 of the piston 110 according to FIGS. 3 and 4 disposed in cavity 31. Cooling oil collector 135 and its placement in cavity 31 are also shown enlarged in FIGS. 5 and 6.

Cooling oil collector 135 is also produced from a spring steel sheet, has an essentially round shape, is provided with a slight curvature, approximately in the shape of a flattened dome, and has a thickness of about 0.8 mm. In contrast to cooling oil collector 35 according to FIGS. 1 and 2, cooling oil collector 135 has a circumferential, spring-elastic edge 136 that is bent axially upward. Furthermore, cooling oil openings 137 and slits 138 are provided, which both increase the elasticity of edge 136 in the radial direction, and serve as additional cooling oil openings. In the exemplary embodiment, cooling oil collector 135 is held between pin boss supports 32 and friction weld bead 34, in the region of lower piston part 12. Cooling oil collector 135 supports itself on pin boss supports 32 in the direction of pin bosses 18. In the direction of upper piston part 11, in the exemplary embodiment shown here, edge 136 touches friction weld bead 34 and supports itself on it, if necessary. Cooling oil collector 135 is disposed in such a manner that its curvature is directed toward upper piston part 11. Depending on the placement of cooling oil collector 135 in cavity 31, the curvature can also be directed toward pin bosses 18.

Of course, cooling oil collector 135 can also be disposed in the region of upper piston part 11, so that it supports itself on or touches the region of the underside of piston crown 13 and friction weld beads 34. In this case, edge 136 is bent axially downward. It is practical if cooling oil channels 33 are disposed in inner support element 25 of lower piston part 12.

In the embodiment shown here, cooling oil collector 135 is furthermore provided with a support element 151. Support element 151 is configured as a separate component. However, it can also be configured in one piece with cooling oil collector 135, and can be produced by punching it out from cooling oil collector 135, for example. It is practical if support element 151 is also produced from a spring steel sheet. Support element 151 has three spring arms 152 that support themselves on the underside of the piston crown 13 of piston 110 in the assembled state. In the exemplary embodiment, spring arms 152 go from a center hub 153, which is attached to cooling oil collector 135 in the longitudinal piston axis. Attachment can take place in any desired manner, for example by means of screwing, riveting, welding, or soldering it on, and the like. It is advantageous if support element 151 is connected with cooling oil collector 135 so that it can rotate. Support element 151 brings about additional spring-elastic securing of the position of cooling oil collector 135 in cavity 31, which is therefore flexibly able to withstand stress during operation.

The function and the assembly of cooling oil collector 135 are the same as described for cooling oil collector 35.

Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 

1. A method for the production of a multi-part piston for an internal combustion engine, comprising the following steps: producing an upper piston part having a piston crown as well as an inner and an outer support element; producing a lower piston part having pin boss supports and pin bosses connected with them, as well as having an inner and an outer support element; inserting a separate cooling oil collector, having at least one cooling oil opening, into the upper piston part or the lower piston part, connecting the upper piston part and the lower piston part so that the inner and outer support elements delimit an outer circumferential cooling channel and a cavity that is open toward the pin bosses and provided with the cooling oil collector.
 2. The method according to claim 1, wherein the cooling oil collector is inserted into a region of the inner support element of the upper piston part, or into a region of the inner support element of the lower piston part.
 3. The method according to claim 1, wherein the inner support elements of the upper piston part and the lower piston part are connected with one another by means of a friction welding method that produces friction weld beads, and wherein the cooling oil collector is held between the friction weld beads and pin boss supports.
 4. The method according to claim 1, wherein the inner support elements of the upper piston part and the lower piston part are connected with one another by means of a friction welding method that produces friction weld beads, and wherein the cooling oil collector is held between the friction weld beads and an underside of the piston crown.
 5. The method according to claim 1, wherein the cooling oil collector is held in the upper piston part or the lower piston part, under spring bias, before upper piston part and lower piston part are connected. 